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Author: Subject: Electrowinning or Thermite?
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[*] posted on 17-6-2012 at 20:11
Electrowinning or Thermite?


Which is the best for recovering the largest / purest amount of the metal when the reaction is done? I'm thinking of using either to make some of the top row transition metals.



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[*] posted on 18-6-2012 at 09:18


The only times thermites give pure(er) products are when the product is a powder, like W or Mo. Metals collected as buttons usually contain several % unreacted Al or Mg plus slag, C, etc.

Plating has the potential to give purer metal but it depends on many factors.

I've done these thermites: B, V, Cr, Cu, Fe, Ni, Mo, W and Mn.

A few products are shown below. From L to R: V, Cr, Cu, B, Mn, W, Ni.

thermites (Small).jpg - 45kB



[Edited on 18-6-2012 by Zan Divine]




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[*] posted on 18-6-2012 at 11:45


In theory Goldschmidt (Thermite) reactions has the potential to produce extremely pure metals (I've seen literature proof of this with a vanadium/Ca reduction). When the Reaction Enthalpy ΔH is very negative and assuming the entropic term (TΔG) is small (a reasonable assumption with thermites), then ΔG ≈ ΔH and with Nernst:

ΔG = - RT ln K with K the equilibibrium constant for the reduction reaction. And if ΔG << 0, then K >>> 1. The activity of the reagents should then be exceedingly small.

In reality the separation between the slag and the formed metal is never perfect and the metal should ideally and at a minimum be de-slagged by melting/recasting.

Zan: how did you get rid of the slag in the case of W? Or did you use Mg or Ca as reductant?

And how did you get powdered Mn?



[Edited on 18-6-2012 by blogfast25]




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[*] posted on 18-6-2012 at 18:17


I would also like to know the story behind the Mn powder. How did you get a powder - a nice, shiny, clean powder as well - out of a molten slag mixture?
Why would Mg or Ca affect slag formation (unless their respective oxides are also slag fluidizers?)




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[*] posted on 19-6-2012 at 06:24


Quote: Originally posted by elementcollector1  

Why would Mg or Ca affect slag formation (unless their respective oxides are also slag fluidizers?)


It's not that. CaO and MgO are easier to remove with strong acids like HCl than Al2O3 (which is IMPOSSIBLE to remove that way). Obviously that would not work for Mn but it would for V or W as these resist HCl easily.




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[*] posted on 19-6-2012 at 06:28


These reactions were all done almost 20 years ago and some details are no longer remembered.

For the manganese, I remember I used commercial MnO2 and Al. This was memorable because this was the most energetic Thermite rxn. I ever performed. I was stunned to see a mixture of metal powder and slag given the quite low mp of Mn. With Mo and W I expected powder, with Mn I didn't. Perhaps the violent nature of this reaction, which ejected material from the graphite crucible, caused heat to be dissipated. The crude material was boiled in NaOH (aq.) to remove aluminium. Manganese metal was separated from Al2O3 by a technique not too different from panning for gold after first removing most slag by filtration through a fine metal screen. Finally, a magnet was dragged through the powder to scavenge Mn-Al, which is apparently magnetic.

Purities for "as-produced" metals ala Goldschmidt are reported as (typically);
95-98% for Mn
~90% for V (imputity primarily Al)
97-99% for Cr (impurities Al, Fe, Si usually)
90% for B, remediated to 93-95% by HCl washing
Cu, Mo, W & Ni rarely made this way, I have no data

The Vanadium was a nice Thermite. It gave the best looking button of the group but it's about 10% Al and essentially worthless. It can't be selectively dissolved out of the V.

The CuO reaction with Al was fierce. Generally, Cu2O is preferred. Indeed, some people have reported explosions with CuO.

Obviously, several of these products pictured (esp. Cu & Ni) have seen some post-reaction processing such as hammering and abrasive cleaning.

I've only had one explosion with Thermite, some 40 years ago in my teens. Just for future reference, a 500 mL beaker half-filled with finely powdered magnesium and powdered iron oxide (don't remember which one) VIOLENTLY exploded after an unusually long induction period w/ KMnO4 & glycerin. I'd estimate that the explosion was equivalent to a partial stick of Dynamite based on the extreme scattering of heavy metal and glass pieces (some 30 -40 lbs in weight) and their trajectory as they rained down.

The lesson? Use coarse powder for Al or Mg reductants.

[Edited on 19-6-2012 by Zan Divine]




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[*] posted on 19-6-2012 at 07:26


Im also intrerested in how the powder was produced.
I once tried useing one of my old grinding wheels (silicon carbide) and a container of water to cool the molten metal as it fell through the bottom of a smelters crucible with a hole in the bottom.
The idea being that the molten metal hit the wheel and sprayed into the water to create the smalest particles I could. I dont know how they do it in industry, anyone know how they do? MM
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[*] posted on 19-6-2012 at 08:21


Quote: Originally posted by mineralman  
I dont know how they do it in industry, anyone know how they do? MM


Mn is now mainly electroplating I think. Then size reduce in inert atmosphere.

One way of obtaining Mn powder is reduction of MnCl2 (ANHYDROUS!)/KCl eutectic melt with Mg. Then remove the MgCl2/KCl slag with a solvent (but not water, with which 'fresh' Mn reacts remarkably well).

Another is MnCl2(s, anhydrous) + Mg === > Mn(l) + MgCl2(l) but this requires a bomb reactor to keep the MgCl2 liquid. The Mn separates out and solidifies on cooling.




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[*] posted on 19-6-2012 at 08:33


A few comments from a dedicated ‘thermiter’ (I’ve a report on thermites for sale on Amazon/eBay) on Zan’s comments.

Mn is almost impossible to ‘do well’ because the BP of Mn is almost the same as the MP of alumina. It’s also a potential flashpowder (MnO2 + Al), largely for that reason.

I’ve seen data on V2O5 + Ca of > 99 % V. Not sure about Al. But ferrovanadium is made by thermite.

CuO is borderline flash, and Cu2O is much to be preferred.

Mg? Only use it with the stablest of oxides but bear in mind its insane MP. Oxides with low HoFs tend to flash with Mg. In fact, more generally I'd say avoid Mg with oxides altogether.

I’ve ‘thermited’ so far Si, Fe, Mn, Cr, Ti, V, Nb, Cu and various alloys: FeSi, FeTi, FeV and CuTi.



[Edited on 19-6-2012 by blogfast25]




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[*] posted on 19-6-2012 at 13:23


For Mn, what of a steel container with a lid? In NighthawkinLight's video for making sodium through magnesiothermal reduction, he mentioned that the gas formed (hydrogen) made a tight vacuum seal inside his container when he placed the mix in a steel can.
Video found here: http://www.youtube.com/watch?v=908rjHQ5mmc




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[*] posted on 19-6-2012 at 20:02


Quote: Originally posted by mineralman  
Im also intrerested in how the powder was produced.
.........
I dont know how they do it in industry, anyone know how they do?

MM


The powder formed in the reaction.

There are different methods. Sometimes ball milling is used. Sometimes a molten metal stream is quenched by injection into a high speed gas stream.





[Edited on 20-6-2012 by Zan Divine]




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[*] posted on 19-6-2012 at 20:17


Quote: Originally posted by blogfast25  

Mg? Only use it with the stablest of oxides but bear in mind its insane MP.

[Edited on 19-6-2012 by blogfast25]


blogfast25, I'm not following....
Mg & Al have almost the same MP.




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[*] posted on 19-6-2012 at 20:48


Well that would explain the why all hell broke loose when the thermite hit my silicon carbide wheel that instantly shattered and the steam/molten metal firework/explosion took place.:o
im glad i only went small scale for that experiment, it scarred the crap out of me.
I still cant believe what posessed me to use water, but it was certainly the single most stupid thing ive ever done, and ive done a lot of stupid things. MM
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[*] posted on 20-6-2012 at 04:50


Quote: Originally posted by elementcollector1  
For Mn, what of a steel container with a lid?


IMHO, forget that unless you’re talking a proper pressure resistant bomb reactor. There is no analogy with what Nighthawk did.

Quote: Originally posted by Zan Divine  

blogfast25, I'm not following....
Mg & Al have almost the same MP.


Sorry, I meant the MP of magnesia being another 300 C higher than that of alumina. That’s a drawback because post-reaction the metal/slag melt freezes up earlier and that leaves less time for complete metal/slag separation.

Mg is more suited to the reduction of chlorides and fluorides, although for the former pressurised reactors are usually needed.




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[*] posted on 20-6-2012 at 07:41


blogfast, thank you for the clarification.

MM, molten metal-steam explosions take place only within a "window" of variables. Staying out of that region is not too difficult. Steam explosions only happen when the rate of heat transfer to the water is excessive. That said, water quenching never gave me usuable material.

I've quenched molten aluminium, brass, copper etc. streams in water. For me, keeping the crucible 3 or 4 feet above the stirred bath is all it takes. This was a naive attempt to get small pellets. It didn't work too well, the particles were rather large (like 1/4" and above mostly) and not at all spherical.

Since your metal was considerably broken up before it hit the water, you were in a much trickier area. Your high surface area molten metal transferred heat to the water too quickly to be dissipated throughout the bulk.

I've long thought about the possibility of using a SS wire wheel to break up the stream but I've never had the time to pursue it much. Given the low cost of granular aluminium, I doubt I ever will.







[Edited on 20-6-2012 by Zan Divine]




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[*] posted on 20-6-2012 at 07:54


Oh and I forgot Co. Nice little nugget I got from that (CoO, very close to the HoF of NiO)



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[*] posted on 20-6-2012 at 08:25


blogfast25,

Is this yours?==>http://developing-your-web-presence.blogspot.com/2008/07/man...

I think my Mn may have boiled. When I look at the particles they are all regular, almost spherical, very fine and silver in color.

You really are the Goldschmidt Scholar of this place.

I missed your earlier question about the W isolation. The honest answer is that I don't remember. Given the extremely small particle size I'm positive that I capitalized on that, but the actual details are lost in the sands of time.

Molybdenum was similar to W but jet black in color.

Did you ever tinker with the idea of Ta thermite?

Concerning the topic of this thread: There is one area that Thermite clearly wins in. Thermite has no limit on the amount of material you can make in a batch. Electrowinning is strictly limited by the equipment.

Thermite, if it gives you what you want, is far cheaper.

Electrowinning will usually give superior samples in terms of homogeneity.

[Edited on 20-6-2012 by Zan Divine]




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[*] posted on 20-6-2012 at 11:48


Zan:

Yep, that post is mine.

So is this one:

http://developing-your-web-presence.blogspot.co.uk/2008/10/o...

On which Theo Gray based his experiments and article:

http://www.popsci.com/node/30347

Yup. Your Mn boiled. I’ve seen it several times. There’s no getting round the Mn BP/alumina MP conundrum, except for pressurising the reactor to keep the Mn liquid (good luck with that at T > 2500 C!)

For a man of your means you may want to try Glatzel’s method. Eutectic melt of MnCl2/KCl. Add fairly coarse Mg powder in small increments (much heat evolves during each addition). After completion heat the mixture to above the MP of Mn for about 1 – 2 h. Then allow to cool. Break open and the Mn regulus is yours.

Tantalising tantalum. Yes, I thermo-calculated a Ta2O5 with Mg reaction. It would fall short of the MP of Ta by a few hundred degrees. In principle that can be overcome by preheating to auto-ignition, But Ta2O5 isn’t easy to get in my neck of the woods.

Too much praise there but I’ll take it :D ...


[Edited on 20-6-2012 by blogfast25]




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[*] posted on 20-6-2012 at 21:24


Of course, that same blog mentions the CaF2 (which I still have yet to obtain! D:<;)
What would be a good 'test' size for the Mn thermite? 20, 30g?
(and how the heck did you ignite these? Mine are stubborn to no end.)




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[*] posted on 21-6-2012 at 00:18


Thanx ZAN, When you mention the use of a wire wheel (STEEL), is this the prefered option when creating small particle size, or just for that aplication alone?

I ask, because I think my carbide wheel may still have been damp, so when the thermite mix hit the damp silicon carbide wheel it instantly shattered. no biggie as I have loads. But I also have some old solid diamond coated wheels by CHRYSTALINE or DIAMOND INT, (ive "YET:D" to break one of these), and being that there solid and don't take on moisture like carbide wheels, could they be used? or am I flogging a dead horse useing a wheel and just use the crucile methods (with/without hole)?.

I have at my disposal, cerium oxide, levagated alumina & tin oxide , silicon & boron carbide. all pure as there polish & grits.
But as I sell mineral specimens and have access to pretty much anything I could want, I can see this as a project that I could get right into.
After the police lift my bail conditions that is:(. MM

OOPS, Almost forgot, look for fluorspar (CaF2) fluorite by its mineal name MM

[Edited on 21-6-2012 by mineralman]

[Edited on 21-6-2012 by mineralman]
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[*] posted on 21-6-2012 at 05:02


Quote: Originally posted by elementcollector1  
Of course, that same blog mentions the CaF2 (which I still have yet to obtain! D:<;)
What would be a good 'test' size for the Mn thermite? 20, 30g?
(and how the heck did you ignite these? Mine are stubborn to no end.)


Up to about 50 g for an initial test, I'd say.

Most surefire ignition I know of is a mixture of KClO3 +2 Al, lit with a piece of Mg ribbon. (K,Na)NO3 + 2 Al will also do.

CaF2: look for it in rockshops, often they sell 'offcuts' which you can grind down yourself. Pottery supplier businesses also stock it, at least some of them...




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[*] posted on 21-6-2012 at 05:50


A collection of poorly arranged thoughts:

MM, I'm not saying that the wire wheel is an approved (or even tested) idea. I was going to try it, but that was before e-Bay made granular Al easy to get & inexpensive.

Unless I needed huge amounts of Al granules I couldn't justify the time and effort. I'd much rather buy the Al and get on to the reason I needed it. Sometimes, the temptation to reinvent the wheel is very strong and it's often a real learning experience but you have to weigh that against the time it takes away from your real goal.

If I were to try again to make granular material, I'd spend a few minutes to look up more details on the air blast method that manufacturers use.

A few details on my long-ago MnO2/Al reaction: I used a graphite crucible with a 3 or 4 to 1 depth to width ratio. I probably had about 50 - 70 grams of mixture. Ignition by KMnO4/glycerin went smoothly. The mixture stayed in the crucible for a short time and then erupted skyward. Burning material was thrown about 20 feet upward and fell to earth in our apartment building's parking lot over an area perhaps 40 feet in diameter. Most of the contents fell right around the crucible, however, and that is where most of the boiled/recondensed Mn was found. This is a potentially dangerous reaction so be prepared.

I see potential in this reaction. In my eyes, any reaction which produces its product as a relatively pure vapor is a desirable thing. I'm not suggesting that anyone try to develope it, but a means of condensing the metal and collecting it would beat separating from slag. Even though it was accidental, my Mn product is a thing of beauty

[Edited on 21-6-2012 by Zan Divine]




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[*] posted on 21-6-2012 at 07:41


Quote: Originally posted by Zan Divine  

A few details on my long-ago MnO2/Al reaction: I used a graphite crucible with a 3 or 4 to 1 depth to width ratio. I probably had about 50 - 70 grams of mixture. Ignition by KMnO4/glycerin went smoothly. The mixture stayed in the crucible for a short time and then erupted skyward. Burning material was thrown about 20 feet upward and fell to earth in our apartment building's parking lot over an area perhaps 40 feet in diameter. Most of the contents fell right around the crucible, however, and that is where most of the boiled/recondensed Mn was found. This is a potentially dangerous reaction so be prepared.

I see potential in this reaction. In my eyes, any reaction which produces its product as a relatively pure vapor is a desirable thing. I'm not suggesting that anyone try to develope it, but a means of condensing the metal and collecting it would beat separating from slag. Even though it was accidental, my Mn product is a thing of beauty

[Edited on 21-6-2012 by Zan Divine]


It helps to include a heat sink like CaF2 or CaO to minimise eruptiveness.

C.K. Gupta in “Metallurgy”:

http://books.google.co.uk/books?id=Tq6MTFXk3cQC&pg=PA457...

... describes a thermite process for Mn in which a mixture of Mn3O4 and aluminium powder (or shavings or whatever) is constantly fed slowly into a crucible where reaction is taking place. According the author the process continues until the crucible is full of liquid manganese. Sounds like a lot of BS for such a prestigious book and author… See p.391.



[Edited on 21-6-2012 by blogfast25]




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[*] posted on 21-6-2012 at 13:42


I don't know, it appears to make sense. Get a reaction going, and sustain it by slowly adding more reactants. As for keeping the heat just right the whole time... *shrug*
... Why not place a cold steel lid a short distance above the reaction (out of reach of the fire)? Manganese gas could cool and redeposit onto there.
I like steel lids. :D Don't know why.

Ooh, NaNO3 is now easy for me! NaOH + NH4NO3 -> NaNO3 + NH3 + H2O

I'd like to use as little nitrate as possible to ignite the test mix, how much? 5g?

[Edited on 21-6-2012 by elementcollector1]




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[*] posted on 22-6-2012 at 04:17


Quote: Originally posted by elementcollector1  


I'd like to use as little nitrate as possible to ignite the test mix, how much? 5g?

[Edited on 21-6-2012 by elementcollector1]


Something like that...




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